This invention relates to a polished-piece holder, and more particularly to a holder for holding a piece to be polished ("hereinafter referred to as "polished piece") such as a silicon wafer, a hard disc or the like.
Manufacturing of a silicon wafer, a hard disc or the like includes a step of polishing a surface thereof into a plane or flat shape. During the polishing step, a polished piece such as a silicon wafer, a hard disc or the like is held on a polished-piece holder called a wafer carrier or a disc carrier for plane polishing.
In general, a polished-piece holder is formed into a disc-like shape while being formed on an outer periphery thereof with a gear and is provided with at least one through-hole in which a polished piece is supportedly fitted. Polishing of the polished piece held in the polished-piece holder is carried out by arranging the polished-piece holder in a polishing apparatus so that the gear formed on the outer periphery thereof may be engaged with an internal gear and a sun gear of the polishing apparatus. Then, the sun gear of the polishing apparatus is rotated to cause planetary motion of the polished-piece holder. This permits a polishing cloth to polish a surface of the polished piece into a plane shape.
Conventionally, the polished-piece holder is constructed of a laminate formed by laminating a plurality of prepregs on each other and heating the laminated prepregs while applying a pressure thereto in a direction of lamination thereof. The prepregs each are made by impregnating a sheet-like fibrous substrate with thermosetting resin, followed by drying of the substrate. Such a laminate is generally used for electrical insulation. The laminates include a cotton cloth-phenolic resin laminate formed by laminating a plurality of prepregs each made by impregnating a fibrous substrate of a cotton cloth with phenolic resin on each other, a glass fiber woven fabric substrate-epoxy resin laminate formed by laminating a plurality of prepregs each made by impregnating a fibrous substrate of a glass fiber woven fabric with epoxy resin on each other, a glass fiber nonwoven fabric substrate-epoxy resin laminate formed by laminating a plurality of prepregs each made by impregnating a fibrous substrate of a glass fiber nonwoven fabric with epoxy resin on each other, a laminate formed by laminating a plurality of prepregs each made by a fibrous substrate of a glass fiber woven fabric with epoxy resin and a plurality of prepregs each made by impregnating a fibrous substrate of a glass fiber non-woven fabric with epoxy resin on each other, and the like. Of the laminates, the cotton cloth-phenolic resin laminate and glass fiber woven fabric substrate-epoxy resin laminate are typically used for the polished-piece holder.
Another polished-piece holder is disclosed in Japanese Patent Application Laid-Open Publication No. 304859/1994, which includes a core layer constituted of a prepreg made by impregnating a fibrous substrate of polyester with thermosetting resin such as epoxy resin or the like. Then, the core layer is formed on each of both surfaces thereof with a surface layer, which is constituted of a prepreg made by impregnating a glass fiber substrate with thermosetting resin. Also, the publication discloses a polished-piece holder having a core layer made of polyurethane resin.
Japanese Patent Application Laid-Open Publication No. 254026/1997 discloses a polished-piece holder of which at least an outer periphery is formed of a glass fiber substrate-epoxy resin laminate, a carbon fiber substrate-epoxy resin laminate or an aramid fiber substrate-resin laminate, to thereby enhance durability of a gear formed on the outer periphery. Unfortunately, the publication is silent concerning a structure of each of the laminates. Judging from the disclosure of the publication, the laminates each are supposed to be used for electrical insulation. In general, a laminate for electrical insulation does not substantially regard wear resistance as important, as compared with that for a polished-piece holder. Thus, the laminate for electrical insulation disclosed includes a surface layer made of a woven fabric substrate.
In general, a polished-piece holder is highly required to exhibit increased wear resistance, thickness accuracy, warpage resistance and dimensional stability. Also, it is recently required to exhibit increased quality and performance. In particular, it is required to exhibit properties of keeping a polished piece from taking deep scratches. Unfortunately, a laminate used for the conventional polished-piece holder fails to exhibit properties of preventing a polished piece from taking deep scratches, because it is inherently used for electrical insulation rather than holding of a polished piece.